Structure for Use in a Corrosive Environment

ABSTRACT

The invention pertains to a structure for use in a humid environment, comprising: a primary structural element, which primary structural element is made of metal and is provided with a coating, which coating has a composition comprising zinc in a content of at least 40 wt % based on the weight of the coating, a secondary structural element, which secondary structural element is made of metal and is provided with a coating, which coating is an alloy comprising aluminum and manganese, in which alloy the content of aluminum and manganese together is at least 90 wt % based on the weight of the coating, which alloy comprises more aluminum by weight than manganese, and wherein the primary structural element and the secondary structural element are in electrical contact with each other.

The invention pertains to a metal structure that is suitable for use ina corrosive environment, for example a structure that is to be arrangedoutdoors.

When a metal structure is used in a corrosive environment, there is arisk that the structural integrity of the structure is compromised bycorrosion of one or more of the structural elements that form part ofthe structure. For example humidity can cause corrosion of the metalsurfaces of the structural elements that are in contact with the humidenvironment directly. In addition to this corrosion due to the contactwith a humid environment itself, arranging the metal structure in ahumid environment may provoke galvanic corrosion of at least one of thestructural elements, in particular when materials with a dissimilarcomposition are used for structural elements that are in electricalcontact with each other. The dissimilar composition can give rise to agalvanic potential difference between the structural components havingthe dissimilar material composition. The moisture from the humidenvironment can act as an electrolyte that closes the electric circuitbetween the structural elements that are in electrical contact with eachother. The closed electric circuit allows electrons to move from onestructural element to the other, therewith causing galvanic corrosion.

It is known to provide metal structural elements with a coating in orderto provide resistance against corrosion of their surfaces that are indirect contact with the corrosive, for example humid, environment. Suchcoatings can be organic coatings, e.g. paint, or metal coatings. Forexample, structural elements made of steel can be provided with a zinccoating by means of galvanizing.

The metallic coating materials that are used for coating structuralelements are usually less noble than the material of the substrate, soin case a galvanic cell forms within the structural element itself, e.g.due to a damaged coating, the coating corrodes rather than substrate, sothat the structural integrity of the structure at least initially iscompromised to a lesser extent. This is called “cathodic protection”.

The downside of the use of a less noble coating material however is thatit can be affected by galvanic corrosion when an other structuralelement that is in electrical contact with the coating, is of a morenoble material. In particular when a zinc coating is used to protectsteel, this regularly occurs, as zinc is less noble than steel.

The “Corrosion Guides” as issued by the National Physical Laboratory ofMiddlesex, United Kingdom, in the series “Corrosion Control” comprise avolume called “Bimetallic Guide”, which discusses galvanic corrosion andrelated design issues. On page 4 of this “Bimetallic Guide”, a table ispresent which shows that zinc can be attacked by galvanic corrosion ifit is combined with aluminum or aluminum alloys.

DE 102007058716 pertains to the mounting of a high alloy steel, such aschromium steel or chromium nickel steel by means of low alloy bolts. Dueto the difference in corrosion potential, galvanic corrosion between thehigh alloy steel and the low alloy steel will occur if no furthermeasures are taken. DE 102007058716 proposes to arrange an intermediateelement between the high alloy steel and the low alloy steel, whichintermediate element is significantly less noble than the high alloysteel and comparable to or less noble than the low alloy steel. Theintermediate element serves as a sacrificial anode for the low alloybolt.

However, a different situation occurs when two or more structuralelements are used that are in electrical contact with each other, whichstructural elements both have to be provided with a coating in order toprotect them from the environment in which they are arranged. In thissituation, the material of the structural elements under the coating isnot particularly relevant for the question whether galvanic corrosionwill occur. The most important is the selection of the coatingmaterials. If the coatings are not carefully selected, galvaniccorrosion may occur even in a situation where the structural elementsare made of the same material.

From the viewpoint of avoiding galvanic corrosion, it would be desirableto use the same coating material for both construction elements, butthis is not always possible, for example if adhesive wear is to beavoided. Furthermore, the use of elements as sacrificial anodes is notalways desired.

The object of the invention is to provide a structure that hasresistance to galvanic corrosion and that at least offers an alternativechoice of a combination of materials, in particular coating materials,as compared to what is known from the prior art.

This object is achieved by a structure for use in a corrosiveenvironment, comprising:

-   -   a primary structural element, which primary structural element        is made of metal and is provided with a coating, which coating        has a composition comprising zinc in a content of at least 40 wt        % based on the weight of the coating,    -   a secondary structural element, which secondary structural        element is made of metal and is provided with a coating, which        coating is an alloy comprising aluminum and manganese, in which        alloy the content of aluminum and manganese together is at least        90 wt % based on the weight of the coating, which alloy        comprises more aluminum than manganese by weight, and,

wherein the primary structural element and the secondary structuralelement are in electrical contact with each other.

The inventors have found that a primary structural element that is madeof metal and is provided with a coating that has a compositioncomprising zinc (Zn) in a content of at least 40 wt % based on theweight of the coating, can in a corrosive environment be combined with asecondary structural element that is also made of metal but has acoating that is an alloy comprising aluminum (Al) and manganese (Mn), inwhich alloy the content of aluminum and manganese together is at least90 wt % based on the weight of the coating, which alloy comprises morealuminum than manganese by weight. If those two structural elements arein electrical contact with each other, and the structure of which thestructural elements form a part is arranged in a corrosive environment,a good resistance against galvanic corrosion is observed, even in casethe corrosive environment is a saline humid environment.

Furthermore, it has been observed that the corrosion resistance forcombination of coating materials according to the invention is largelyindependent of the relative size of the surface areas of the primary andsecondary structural elements.

The structural elements being in electrical contact with each othermeans that the two structural elements are not electrically insulatedfrom each other. For example, electrical contact is present when thereis direct physical contact between the metal or metallic coating of theprimary structural element and the metal or metallic coating of thesecondary structural element. In an other example, electrical contact ispresent when the metal or metallic coating the primary structuralelement is connected to the metal or metallic coating of the secondarystructural element via one or more conductive elements, for example viaa metallic bolt or metal rings. In general, electrical contact ispresent when a path is provided that allows electrons to move from theprimary structural element (including its coating) to the secondarystructural element (including its coating) or vice versa. This path doesnot have to be a closed loop within the structure, it is for examplepossible that the path can be closed by the presence of an electrolyte,e.g. saline water.

In particular, good resistance to galvanic corrosion has been observedwhen the aluminum content in the coating of the secondary structuralelement is at least about 75 wt % based on the weight of the coating.

Preferably, the aluminum content in the coating of the secondarystructural element is at least about 75 wt % based on the weight of thecoating, and at least about 80 wt % of the remainder of the coating ismanganese.

Preferably, the manganese content in the coating of the secondarystructural element is between about 1 wt % and about 25 wt %, morepreferably between about 5 wt % and about 18 wt %, based on the weightof the coating.

Examples of compositions of the aluminum manganese coating are: about81-83 wt %, e.g. 82 wt %, aluminum, based on the weight of the coatingand about 19-17 wt %, e.g. 18 wt %, manganese, based on the weight ofthe coating; about 84-86 wt %, e.g 85 wt %, aluminum, based on theweight of the coating and about 16-14 wt %, e.g. 15 wt %, manganese,based on the weight of the coating; or about 94-96 wt %, e.g. 95 wt %,aluminum, based on the weight of the coating and about 6-4 wt %, e.g. 5wt %, manganese, based on the weight of the coating.

Optionally, the aluminum manganese coating of the secondary structuralelement consists of aluminum, manganese and inevitable impurities.

The aluminum manganese alloy coating of the secondary structural elementaccording to the invention also has good properties with respect toenhancing the corrosion resistance against corrosion due to directcontact with the corrosive environment. The addition of manganese to thealuminum has an effect on the morphology of the coating layer. Itresults in a dense structure with small crystallites. The grain size isgenerally smaller than in a pure aluminum coating that is depositedusing electrochemical deposition from an ionic liquid.

The dense morphology of the aluminum manganese coating of the secondarystructural element provides a good protection for the material of thesubstrate, as it makes a strong barrier between the substrate and theenvironment.

The aluminum manganese alloy that is used for the coating of thesecondary structural element is less noble than steel, in particularless noble than the types of mild steel that are generally used inconstruction. So, in case a secondary element is made of steel, and thealuminum manganese coating on it becomes damaged, the coating providescathodic protection for the steel substrate of the secondary structuralelement.

The aluminum manganese alloy is nobler than the zinc or zinc containingcoating of the primary structural element. This in contrast to aluminumalloys such as aluminum zinc alloys, aluminum magnesium alloys, aluminumtin alloys or aluminum silicon alloys, which are less noble than zinc.

Preferably, the thickness of the coating of the secondary structuralelement is between about 1.5 μm and about 100 μm, preferably betweenabout 5 μm and about 30 μm.

In a possible embodiment, the metal of the primary structural elementand/or the secondary structural element is steel, for example mildsteel. According to a commonly used definition, “mild steel” is the sameas plain carbon steel.

In a possible embodiment, the metal of the primary structural elementand/or the secondary structural element is steel with a carbon contentof 0.5% or less, optionally carbon steel with a carbon content of 0.5%or less.

In a possible embodiment, the metal of the primary structural elementand/or the secondary structural element is low alloy steel, which lowalloy steel optionally contains 8% or less alloying elements.

In a possible embodiment, the metal of the primary structural elementand/or the secondary structural element is steel, which steel is notstainless steel.

In a possible embodiment, the metal of the primary structural element orthe secondary structural element is carbon steel with a carbon contentof 0.5% or less, and the metal of the other of the primary structuralelement and the secondary structural element is low alloy steel, whichlow alloy steel optionally contains 8% or less alloying elements.

Suitable coatings for the primary structural element for example includezinc-coatings (e.g. of the type that is generally indicated in the art,for example in the draft European standard dEN10346:2013, by “Z”),zinc-iron alloy coatings (e.g. of the type that is generally indicatedin the art, for example in the draft European standard dEN10346:2013, by“ZF”), zinc-aluminum alloy coatings (e.g. of the type that is generallyindicated in the art, for example in the draft European standarddEN10346:2013, by “ZA”), zinc-magnesium alloy coatings (e.g. of the typethat is generally indicated in the art, for example in the draftEuropean standard dEN10346:2013, by “ZM”) and aluminum-zinc alloycoatings (e.g. of the type that is generally indicated in the art, forexample in the draft European standard dEN10346:2013, by “AZ”).

Examples of suitable coatings for the primary structural element includecoatings that can be obtained by galvanization (e.g. batchgalvanization, hot-dip galvanization or electrogalvanization), coatingsof Aluzinc®, coatings of Magnelis® and zinc coatings having at leastabout 90 wt % of pure zinc.

A possible coating material for the primary structural element is ahot-dip zinc coating (Z), which can be applied on a first metalsubstrate by immersing the first metal substrate in a molten bathcontaining a zinc content of at least about 99 wt % of the molten bath.Such a coating generally comprises about 99 wt % to about 99.9 wt % ofzinc (based on the weight of the coating), the balance generally beingaluminum and inevitable impurities. By providing the first metalsubstrate with such a coating, a primary structural element according tothe invention can be obtained.

A possible coating material for the primary structural element is ahot-dip zinc-iron alloy coating (ZF), which can be applied on a firstmetal substrate by applying a zinc coating by immersing the first metalsubstrate in a molten bath containing a zinc content of at least about99 wt % and a subsequent annealing which produces an iron-zinc coatingwith an iron content of normally about 8 wt % to about 12 wt % (based onthe weight of the coating), the balance being mainly zinc. By providingthe first metal substrate with such a coating, a primary structuralelement according to the invention can be obtained.

A possible coating material for the primary structural element is ahot-dip zinc-aluminum alloy coating (ZA), which can be applied on afirst metal substrate by immersing the first metal substrate in a moltenbath which is composed of zinc and approximately 5 wt % aluminum andsmall amounts of mischmetal. Such a coating generally comprises about 5wt % of aluminum (based on the weight of the coating), the balancegenerally being zinc and the mischmetal. By providing the first metalsubstrate with such a coating, a primary structural element according tothe invention can be obtained.

A possible coating material for the primary structural element is ahot-dip zinc-magnesium coating (ZM), which can be applied on a firstmetal substrate by passing the first metal substrate through a moltenzinc bath with aluminum and magnesium contents in sum of about 1.5 wt %to about 8 wt %, the remainder being mainly zinc. Such a coatinggenerally comprises aluminum and magnesium contents in sum of about 1.5wt % to 8 about wt % (based on the weight of the coating), the remainderbeing mainly zinc. By providing the first metal substrate with such acoating, a primary structural element according to the invention can beobtained.

A possible coating material for the primary structural element is ahot-dip aluminum-zinc alloy coating (AZ), which can be applied on afirst metal substrate by immersing the first metal substrate in a moltenbath which is composed of about 55 wt % aluminum, about 1.6 wt % siliconand the balance zinc. Such a coating generally comprises about 55 wt %aluminum, about 1.6 wt % silicon (based on the weight of the coating)and the balance zinc. By providing the first metal substrate with such acoating, a primary structural element according to the invention can beobtained.

A possible coating material for the primary structural element comprisesabout 2-8 wt % aluminum, about 0-5 wt % magnesium, about 0-0.3 wt %alloying elements, the balance being zinc and inevitable impurities.Such a coating for example comprises about 93.5 wt % zinc, about 3.5 wt% aluminum and about 3 wt % magnesium.

Another possible coating material for the primary structural elementcomprises about 43 wt % zinc, about 55 wt % aluminum and about 1.5-2 wt% silicon.

In general, a structure of the type to which the invention pertainscomprises at least two types of structural elements. The first type ofstructural elements for example comprises a metal beam, profile, rod,strip, and/or sheet. Such structural elements form the framework of thestructure and bear the mechanical loads that are exerted on thestructure. The second type of structural elements comprises fasteners,supports and the like (e.g. bolts, nuts, screws, clips, clamps). Theyhold the structural elements of the first type together by connectingthem to each other. The structural elements of the second type canalternatively or in addition be used for connecting other objects to thestructural elements of the first type. Such objects could for example besolar panels, switch boxes or other electrical equipment, cables and/orsensors, or e.g. an exhaust system of a vehicle.

The primary structural element according to the invention can be astructural element of the first type or a structural element of thesecond type. The secondary structural element according to the inventioncan be a structural element of the first type or a structural element ofthe second type.

Optionally, the primary structural element according to the invention isa structural element of the first type and the secondary structuralelement according to the invention is a structural element of the secondtype.

Optionally, the structure according to the invention comprises a primarystructural element according to the invention which is a structuralelement of the first type, which is connected to a structural element ofthe first type of a different material (e.g. stainless steel oraluminum). In this possible embodiment, both structural elements of thefirst type are connected to each other by means of a structural elementof the second type, which is a secondary element according to theinvention. Such a structure could for example comprise a beam that isprovided with a coating that has a composition comprising zinc in acontent of at least 40 wt % based on the weight of the coating, which isconnected to a beam of for example stainless steel or aluminum by meansof a bolt (or a bolt and a nut), which bolt is provided with a coatingthat is an alloy comprising aluminum and manganese, in which alloy thecontent of aluminum and manganese together is at least 90 wt % based onthe weight of the coating, which alloy comprises more aluminum thanmanganese by weight.

Optionally, the primary structural element according to the invention isa structural element of the first type and the secondary structuralelement according to the invention is also a structural element of thefirst type.

Optionally, the primary structural element according to the invention isa structural element of the second type and the secondary structuralelement according to the invention is a structural element of the firsttype.

Optionally, the primary structural element according to the invention isa structural element of the first type and the structure furthercomprises one or more secondary structural elements according to theinvention that are a structural element of the first type as well ascomprises one or more secondary structural elements according to theinvention that are a structural element of the second type.

Optionally, the structure according to the invention comprises a primarystructural element according to the invention which is a structuralelement of the first type and a secondary structural element accordingto the invention which is a structural element of the second type, andan object, e.g. a functional device, that is connected to the primarystructural element by means of the secondary structural element. Such astructure could for example comprise a beam that is provided with acoating that has a composition comprising zinc in a content of at least40 wt % based on the weight of the coating, and a further object (e.g afunctional device like a solar panel, a support for a solar panel, aswitch box or other type electrical equipment, a cable and/or sensor, ore.g. an exhaust system of a vehicle) which is of a different material(e.g. stainless steel or aluminum), which further object is connected tothe beam with the zinc coating by means of a bolt (or a bolt and a nut)that is provided with a coating that is an alloy comprising aluminum andmanganese, in which alloy the content of aluminum and manganese togetheris at least 90 wt % based on the weight of the coating, and which alloycomprises more aluminum than manganese by weight.

It has been observed that the corrosion resistance for combination ofcoating materials according to the invention is largely independent ofthe relative size of the surface areas of the primary and secondarystructural elements. So, the primary structural element can have alarger surface area than the secondary structural element, or theprimary structural element can have a smaller surface area than thesecondary structural element, or the primary structural element and thesecondary structural element can have substantially the same surfacearea. This is a further advantage of the invention, as many knowncorrosion resistant coating material combinations require that onecoating material of the combination has to the used for the structuralelement with larger surface area and the other coating material of thecombination has to the used for the structural element with the smallersurface area.

In a possible embodiment, the primary structural element has a largersurface area than the secondary structural element. If in such anembodiment galvanic corrosion would take place between the coatings ofthe primary and secondary structural elements despite the relativelyhigh corrosion resistance of this combination of coatings, then thecoating on the primary structural element will be affected. This isbecause the coating of the secondary structural element is slightlynobler than the coating of the primary structural element. However, asthe primary structural element has the larger surface area, thecorrosion will be more spread out over the surface than when the primarystructural element would have a smaller surface area than the secondarystructural element.

A structure according to the invention can for example be used as amounting system for solar panels or be a part of such a mounting system.It can however also be used in other structures, like bridges, powerpylons, cranes, support structures, or in automotive applications suchas underbodies or chassis or other parts of cars or trucks, or parts ofother vehicles, e.g. motorcycles.

The structure according to the invention can be arranged or used in acorrosive environment, for example a humid environment, optionally asaline humid environment, for example outdoors, for example on land orin a marine environment or on land in an area close to the sea. Forexample, the structure can be a support structure for solar panels orcan be used as a mounting system for solar panels or can be a part ofsuch a mounting system, allowing to arrange solar panels in corrosiveenvironment, for example in areas close to the sea or even in a marineenvironment, e.g. on board of a ship or drilling rig. For example, thestructure can be a vehicle or a part of a vehicle.

The coatings of the primary and secondary structural elements can beapplied using methods that are generally known in the art. Optionally,the aluminum manganese alloy coating is applied to the secondarystructural element by means of electrodeposition from an ionic liquid.By using this method for applying the aluminum manganese coating, adense coating layer with small crystallites and little or no cracks orvoids can be obtained.

It is desirable that the aluminum manganese coating of the secondarystructural element adheres well to the substrate. It has been found thatin case electrodeposition from an ionic liquid is used to apply thealuminum manganese coating, it is advantageous to give the substrateonto which the aluminum manganese coating will be applied a pretreatmentby means of etching, optionally by means of electrochemical etching,optionally by means of electrochemical etching in an ionic liquid.

The etching roughens the surface of the substrate, which results in abetter adhesion of the coating onto the substrate. The etching alsoremoves for example oxides or contamination from the surface of thesubstrate. This also improves the adherence of the coating.

It is possible to carry out the electrochemical etching in the same typeof ionic liquid as the ionic liquid in which the electrochemicaldeposition of the aluminum manganese coating takes place. It is evenpossible to carry out the electrochemical etching in the same bath ofionic liquid as the bath of ionic liquid in which the electrochemicaldeposition of the aluminum manganese coating takes place.

In a possible embodiment, a voltage in the range of about 0.5 V to about1.5 V versus an aluminum electrode is used during the electrochemicaletching, for example during an etch time of about 1 second to about 90seconds.

In a possible embodiment, prior to carrying out the pretreatment of thesubstrate by etching, the substrate is cleaned and/or degreased. Thiscan for example be done by means of an acid, such as sulfuric acid.

In a possible embodiment, the ionic liquid is stirred or otherwiseagitated during the electrochemical deposition of the aluminum manganesecoating onto the substrate to form the secondary structural element.This prevents that the surface is damaged due to a lack of reactivesubstances near the surface to form the coating.

In a possible embodiment, the ionic liquid is a combination of1-ethyl-3-methylimidazoliumchloride (EMIMCl) and aluminum chloride(AlCl₃), preferably in a mol ratio of about 1:1.5, and further comprisesMnCl₂, preferably between about 0.01 wt % and about 5 wt % MnCl₂,optionally between about 0.02 and about 1 wt % MnCl₂, based on theweight of the ionic liquid.

In a possible embodiment, the current density during the deposition ofthe aluminum manganese coating is between about 2 A/dm² and about 7A/dm², preferably about 4 A/dm².

In a possible embodiment, the process of the deposition of the aluminummanganese coating is carried out at a process temperature between about45° C. and about 100° C., optionally between 75° C. and 95° C.,optionally at about 90° C.

In a possible embodiment, the secondary structural element is cleanedafter the deposition of the aluminum manganese coating, for example bywater and/or acetone.

In a possible embodiment, the deposition time of the deposition of thealuminum manganese coating is between about 1 minute and about 60minutes, optionally between about 3 minutes and about 50 minutes,optionally between about 7 minutes and about 15 minutes, optionallybetween about 8 minutes and about 12 minutes, optionally about 10minutes.

The invention will be described in more detail below under reference tothe drawing, in which in a non-limiting manner exemplary embodiments ofthe invention will be shown.

The drawing shows in:

FIG. 1: a first example of a structure according to the invention,

FIG. 2: a second example of a structure according to the invention,

FIG. 3: an example of structures according to the invention being usedin a mounting system for a solar panel,

FIG. 4: a first image of the aluminum manganese coating of the secondarystructural element obtained by electrochemical deposition from an ionicliquid,

FIG. 5: a second image of the aluminum manganese coating of thesecondary structural element obtained by electrochemical deposition froman ionic liquid,

FIG. 6: results of accelerated galvanic corrosion tests that have beencarried out on different combinations of materials in a saline humidenvironment, shown as photos of bolts in a profile,

FIG. 7: results of the accelerated galvanic corrosion tests of FIG. 6,photos of the profile only,

FIG. 8: results of further accelerated corrosion tests that have beencarried out on bolts of different materials.

FIG. 1 shows a first example of a structure according to the invention.

The structure of FIG. 1 has a primary structural element 1, which inthis example is a beam. It also has a secondary structural element 2,which also is a beam. The primary structural element 1 and the secondstructural element 2 are in electrical contact with each other. When thestructure is arranged in a corrosive, e.g. a humid, environment, themoisture will act as an electrolyte, closing the electric circuitbetween the primary structural element 1 and the secondary structuralelement 2. If the moisture is saline, it will be an effectiveelectrolyte, increasing the risk of galvanic corrosion.

The primary structural element 1 and the secondary structural element 2can be fixed to each other, e.g. by welds or by bolts, but this is notnecessary as long as they are in electrical contact with each other,e.g. via electrically conductive structural elements.

Both beams are made of metal, e.g. steel, and are provided with acoating.

The coating of the primary structural element 1 is a metal coating, ofwhich a main component is zinc (Zn). The coating of the primarystructural element comprises at least 40 wt % zinc, based on the weightof the coating. The primary structural element 1 can for example have azinc-coating (e.g. Z-type in accordance with draft European StandarddEN10346:2013), a zinc-iron alloy coating (e.g. ZF-type in accordancewith draft European Standard dEN10346:2013), a zinc-aluminum coating(e.g. ZA-type in accordance with draft European Standard dEN10346:2013)a zinc-magnesium alloy coating (e.g. ZM-type in accordance with draftEuropean Standard dEN10346:2013), or an aluminum-zinc alloy coating(e.g. AZ-type in accordance with draft European Standard dEN10346:2013).

The coating of the secondary structural element 2 is an aluminummanganese coating, which means that the material of the coating is analloy comprising aluminum and manganese. The coating comprises morealuminum than manganese by weight and the content of aluminum andmanganese together is at least 90 wt % based on the weight of thecoating.

Preferably, the aluminum content in the coating of the secondarystructural element 2 is at least about 75 wt % based on the weight ofthe coating. Optionally, at least about 80 wt % of the remainder of thecoating is manganese. For example, the aluminum manganese coating of thesecondary structural element comprises about 81-83 wt %, e.g. 82 wt %,aluminum, based on the weight of the coating and about 19-17 wt %, e.g.18 wt %, manganese, based on the weight of the coating; about 84-86 wt%, e.g 85 wt %, aluminum, based on the weight of the coating and about16-14 wt %, e.g. 15 wt %, manganese, based on the weight of the coating;or about 94-96 wt %, e.g. 95 wt %, aluminum, based on the weight of thecoating and about 6-4 wt %, e.g. 5 wt %, manganese, based on the weightof the coating.

FIG. 2 shows a second example of a structure according to the invention.

The structure of FIG. 2 comprises two strips 4. These strips are primarystructural elements, and are made of metal and provided with a coatingthat has a zinc content of at least 40 wt % based on the weight of thecoating. For example, the strips 4 are galvanized or otherwise providedwith for example a zinc-coating (e.g. Z-type in accordance with draftEuropean Standard dEN10346:2013), a zinc-iron alloy coating (e.g.ZF-type in accordance with draft European Standard dEN10346:2013), azinc-aluminum coating (e.g. ZA-type in accordance with draft EuropeanStandard dEN10346:2013) a zinc-magnesium alloy coating (e.g. ZM-type inaccordance with draft European Standard dEN10346:2013), or analuminum-zinc alloy coating (e.g. AZ-type in accordance with draftEuropean Standard dEN10346:2013).

The strips 4 are connected to each other by a bolt 5. The bolt isprovided with a coating that is an alloy comprising aluminum andmanganese, wherein the coating comprises more aluminum than manganese byweight and the content of aluminum and manganese together is at least 90wt % based on the weight of the coating. In the structure of FIG. 2,bolt 5 is a secondary structural element.

Preferably, the aluminum content in the coating of the bolt 5 is atleast about 75 wt % based on the weight of the coating. Optionally, atleast about 80 wt % of the remainder of the coating is manganese. Forexample, the aluminum manganese coating of the bolt comprises about81-83 wt %, e.g. 82 wt %, aluminum, based on the weight of the coatingand about 19-17 wt %, e.g. 18 wt %, manganese, based on the weight ofthe coating; about 84-86 wt %, e.g. 85 wt %, aluminum, based on theweight of the coating and about 16-14 wt %, e.g. 15 wt %, manganese,based on the weight of the coating; or about 94-96 wt %, e.g. 95 wt %,aluminum, based on the weight of the coating and about 6-4 wt %, e.g. 5wt %, manganese, based on the weight of the coating.

FIG. 3 shows an example of structures according to the invention beingused in a mounting system for a solar panel, in side view.

In the embodiment of FIG. 3, a solar panel 10 is mounted onto a supportstructure 8. The support structure comprises a first leg 20, a secondleg 22 and a slanting beam 21 that extends between the first leg 20 andthe second leg 22. The slanting beam 21 is in this embodiment welded tothe first leg 20 and the second leg 22 to form a portal. Although notvisible in FIG. 3, the support structure comprises a second portalsimilar the one that is made up by the first leg 20, the slanting beam21 and the second leg 22. This second portal is arranged next to theportal that is made up by the first leg 20, the slanting beam 21 and thesecond leg 22.

The support structure 8 further comprises a bottom strip 23 and a topstrip 24. The bottom strip 23 and the top strip 24 extend from theportal that is made up by the first leg 20, the slanting beam 21 and thesecond leg 22 to the second portal. The bottom strip 23 and the topstrip 24 are arranged adjacent to the solar panel 10, and therewithprevent that the solar panel 10 slides up or down on the slanting beam21.

The bottom strip 23 and the top strip 24 are connected to the portalthat is made up by the first leg 20, the slanting beam 21 and the secondleg 22 and the second portal by bolts 30.

The support structure 8 further comprises at least one side plate 25.The side plate 25 is connected to the slanting beam 21 by a bolt 32 andto the solar panel 10 by a bolt 31. The side plate 25 prevents the solarpanel from moving sideways over the slanting beam 21.

A cable 11 connects the solar panel 10 to a switchbox 12. The switchbox12 is connected to the first leg 20 by a bottom support profile 27 and atop support profile 26. The top support profile 26 and the bottomsupport profile 27 are connected to the switchbox by bolts 33 and to thefirst leg 20 by bolts 34.

The cable 11 is strapped to the first leg by a metallic cable strap 35.

In the support structure 8 of FIG. 3, the first leg 20, the second leg22, the slanting beam 21, the second portal, the bottom strip 23, thetop strip 24, the side plate 25, the top support profile 26 and thebottom support profile 27 are structural elements of the first type. Atleast one of them, but preferably all of them are primary structuralelements in accordance with the invention. The first leg 20, the secondleg 22, the slanting beam 21, the second portal, the bottom strip 23,the top strip 24, the side plate 25, the top support profile 26 and/orthe bottom support profile 27 qualify as primary structural element inaccordance with the invention if they are made of metal and providedwith a coating that has a composition with a zinc contents of at least40 wt %. So, for example, they are galvanized or otherwise provided withfor example a zinc-coating (e.g. Z-type in accordance with draftEuropean Standard dEN10346:2013), a zinc-iron alloy coating (e.g.ZF-type in accordance with draft European Standard dEN10346:2013), azinc-aluminum coating (e.g. ZA-type in accordance with draft EuropeanStandard dEN10346:2013) a zinc-magnesium alloy coating (e.g. ZM-type inaccordance with draft European Standard dEN10346:2013), or analuminum-zinc alloy coating (e.g. AZ-type in accordance with draftEuropean Standard dEN10346:2013).

In the support structure 8 of FIG. 3, the bolts 30, 31, 32, 33, 34 andthe metal strap 35 are structural elements of the second type. At leastone of them, but preferably all of them are secondary structuralelements in accordance with the invention. The bolts 30, 31, 32, 33, 34and/or the metal strap 35 qualify as secondary structural element inaccordance with the invention if they are provided with a coating whichis an alloy comprising aluminum and manganese as the main components,which coating comprises more aluminum than manganese by weight and thecontent of aluminum and manganese together is at least 90 wt %.

Preferably, the aluminum content in the coating of the bolts 30, 31, 32,33, 34 and the metal strap 35 is at least 75 wt %. For example, thealuminum manganese coating of the bolts 30, 31, 32, 33, 34 and the metalstrap 35 comprises about 82 wt % aluminum and about 18 wt % manganese,or about 85 wt % aluminum and about 15 wt % manganese or about 95 wt %aluminum and about 5 wt % manganese.

Optionally, not all of the first leg 20, the second leg 22, the slantingbeam 21, the second portal, the bottom strip 23, the top strip 24, theside plate 25, the top support profile 26 and the bottom support profile27 are provided with a coating which contains at least 40 wt % zinc.Optionally, not all bolts 30, 31, 32, 33, 34 and/or the metal strap 35are provided with a coating which is an alloy comprising aluminum andmanganese as the main components, which coating comprises more aluminumthan manganese by weight and the content of aluminum and manganesetogether is at least 90 wt %. However, the support structure 8 comprisesat least one primary structural element that is made of metal and thatis provided with a coating which has a composition that comprises atleast 40 wt % zinc, and at least one secondary structural element thatis in electrical contact with this particular primary structuralelement, which secondary structural element is made of metal and isprovided with a coating which is an alloy comprising aluminum andmanganese as the main components, the coating of said secondarystructural element comprising more aluminum than manganese and thecontent of aluminum and manganese together being at least 90 wt %.

FIG. 4 and FIG. 5 show images of the aluminum manganese coating of thesecondary structural element obtained by electrochemical deposition froman ionic liquid, as is part of the method of claim 14. The images ofFIG. 4 and FIG. 5 have been obtained by an electron microscope. The finegrained and dense structure of the aluminum manganese coating is clearlyvisible.

A structure according to the invention can for example be manufacturedby a method in accordance with claim 14, optionally according to acombination of claim 14 with the dependent claims 15-22.

According to this method, a first metal substrate is provided with acoating that comprises at least 40 wt % zinc based on the weight of thecoating. This can be done by methods known in the art, such asgalvanizing, e.g. batch galvanizing, hot-dip galvanizing orelectrogalvanizing. Thereby, a primary structural element according tothe invention is obtained.

Further, a second metal substrate is provided onto which a coating willbe applied that is an alloy comprising aluminum and manganese, whichalloy comprises more aluminum than manganese by weight and in whichalloy the content of aluminum and manganese together is at least 90 wt %based on the weight of the coating.

Preferably, the second metal substrate is cleaned and/or degreasedbefore the other method steps are carried out. The cleaning and/ordegreasing can be carried out for example by using an acid, e.g.sulfuric acid.

After the optional cleaning and/or degreasing, the second metalsubstrate is etched, optionally electrochemically etched, such that thesurface of the substrate is roughened and/or contamination and/or oxidesare removed from the surface of the second substrate as well.

The second metal substrate is arranged in a bath of ionic liquid. Thiscan be done either before or after the electrochemical etching. If thesecond substrate is arranged in the bath of ionic liquid before theetching, the etching can be carried out in this bath of ionic liquid inthe form of electrochemical etching.

After the etching, the second substrate can be removed from the bath ofionic liquid and transferred to a second bath of ionic liquid, in whichthe deposition of the aluminum manganese coating is applied.Alternatively, the deposition of the aluminum manganese coating on thesecond metal substrate can take place in the same bath as in which theelectrochemical etching took place.

Alternatively, it is possible that the etching does not take place in anionic liquid but for example in a aqueous solution. The etching does nothave to be an electrochemical etching, it can for example alternativelybe chemical etching. In case the etching does not take place in theionic liquid from which the aluminum manganese coating is deposited, thesecond metal substrate is arranged in the bath of ionic liquid after theetching.

In case electrochemical etching is applied, the etching can for examplebe carried out at a voltage in the range of about 0.5V to about 1.5Vversus an aluminum electrode, during about 1 to about 90 seconds.

After the etching, the aluminum manganese coating is applied to thesecond substrate. A source of aluminum and manganese is provided and thecoating is deposited by means of electrodeposition from an ionic liquid,which for example is a combination of1-ethyl-3-methylimidazoliumchloride (EMIMCl) and aluminum chloride(AlCl₃), and further comprises MnCl₂. The mol ratio between1-ethyl-3methylimidazoliumchloride (EMIMCl) and aluminum chloride(AlCl₃) is preferably between about 1:1 and about 1:2.5, more preferablyabout 1:1.5. Preferably, the content of MnCl₂ is between about 0.01 wt %and about 5 wt %, optionally between 0.02 and 1 wt %, based on theweight of the ionic liquid.

Optionally, the deposition takes place in waterfree conditions, forexample under an argon atmosphere. Such conditions are in particularsuitable when a combination of 1-ethyl-3-methylimidazoliumchloride(EMIMCl) and aluminum chloride (AlCl₃), further comprising MnCl₂ is usedto deposit the aluminum manganese coating from.

Preferably, during the deposition of the aluminum manganese coating, theionic liquid is agitated, for example by stirring it. This ensures thatsufficient reactive components to form the aluminum manganese coatingare available in the vicinity of the surface of the second metalsubstrate.

It was found that a suitable current density for the deposition processof the aluminum manganese coating is between about 2 A/dm² and about 7A/dm², preferably about 4 A/dm².

Optionally, the thickness of the deposited aluminum manganese coating isbetween about 1.5 μm and about 100 μm, preferably between about 5 μm andabout 30 μm.

After the deposition of the aluminum manganese coating, the secondsubstrate has become a secondary structural element in accordance withthe invention.

After the deposition of the aluminum manganese coating, the secondsubstrate is taken out of the bath of ionic liquid and optionallycleaned, for example by acetone and/or water.

Optionally, the electrochemical etching of the second metal substrateand/or the electrodeposition of the aluminum manganese coating onto thesecond metal substrate take place at a process temperature between about45° C. and about 100° C., optionally between about 75° C. and about 95°C., optionally at about 90° C.

Connecting the primary structural element and the secondary structuralelement to each other such that the primary structural element and thesecondary structural element are in electrical contact with each otherfinishes the manufacturing of the structure according to the invention.

Optionally, the coating of the primary structural element is applied inone of the following ways:

-   -   by immersing the first metal substrate in a molten bath        containing a zinc content of at least about 99 wt %,    -   by applying a zinc coating by immersing the first metal        substrate in a molten bath containing a zinc content of at least        about 99 wt % and a subsequent annealing which produces an        iron-zinc coating with an iron content of normally about 8 wt %        to about 12 wt % based on the weight of the coating,    -   by immersing the first metal substrate in a molten bath which is        composed of zinc and approximately 5 wt % aluminium and small        amounts of mischmetal.    -   by passing the first metal substrate through a molten zinc bath        with aluminium and magnesium contents in sum of about 1.5 wt %        to about 8 wt %.    -   by immersing the first metal substrate in a molten bath which is        composed of about 55 wt % aluminium, about 1.6 wt % silicon and        the balance zinc.

FIG. 6 and FIG. 7 show results of accelerated cyclic galvanic corrosiontests that have been carried out on different combinations of materialsin a humid and saline environment.

The accelerated corrosion tests have been carried out as follows: a boltof stainless steel, a bolt with an aluminum manganese coating inaccordance with the invention and several types of galvanized bolts werearranged in a profile provided with a ZM-type coating about 93.5 wt %Zn, about 3.5 wt % Al and about 3 wt % Mg.

The profile with the bolts was subjected to the following test cycle:

-   -   24 hours salt spray test in accordance with ASTM_B 117), with 5%        NaCl at 35° C.,    -   four days at a condensate water climate, each day having 8 hours        at 40° C. and 95% relative humidity and 16 hours at 20° C. and        75% relative humidity,    -   two days at room climate, at 20° C. and 65% relative humidity.

This test cycle was repeated six times, so a total of six weeks testingtook place.

The stainless steel bolt and galvanized bolts that were used wereregular commercially available bolts. Chemical analysis showed thestainless steel bolt was made of a 304-type stainless steel, havingabout 18 wt % Cr, about 8 wt % Ni, about 2 wt % Cu, about 1.7 wt % Mn,about 0.25 wt % Si and about 0.25 wt % Mo as alloying elements. It isidentified by the supplier as DIN 916 inox.

The galvanized bolts are in FIG. 6 identified by the text on therespective heads of the bolts. The bolt indicated by “NORM 8.8” isgalvanized according to EN ISO 4042 and EN 12329 as supplied byEriks+Baudoin and Fabory. The coating on this bolt was about 19 μm thickand contained Zn, Al, Si and Ti.

The bolt indicated by “HBS 8.8U” is galvanized according to ISO 10684 assupplied by Eriks+Baudoin and Fabory. The coating on this bolt was about56 μm thick and contained Zn and Pb.

The bolt indicated by “CW 8.8” is galvanized. The coating on this boltwas about 7 μm thick and contained mainly Zn.

The bolt indicated by “JD 8.8” is electrogalvanized according to EN ISO4042 and EN 12329. The coating on this bolt was about 7 μm thick andcontained mainly Zn.

FIG. 6 shows the combination of the profile and the bolt. Column A ofFIG. 6 shows the situation at the start of the test. Column B of FIG. 6shows the situation after one week and column C of FIG. 6 shows thesituation after six weeks, so at the end of the test.

FIG. 7 shows the profile only. Picture A of FIG. 7 shows the profilenear the hole in which the stainless steel bolt was present during thetest. Picture B of FIG. 7 shows the profile near the hole in which thebatch galvanized NORM bolt was present during the test. Picture C ofFIG. 7 shows the profile near the hole in which the galvanized HBS 8.8ubolt was present during the test. Picture D of FIG. 7 shows the profilenear the hole in which the electrogalvanized JD 8.8 bolt was presentduring the test. Picture E of FIG. 7 shows the profile near the hole inwhich the bolt with the aluminum manganese coating according to theinvention was during present the test.

After the full test of six weeks, the combination of the ZM-coatedprofile and the stainless steel bolt showed white corrosion of theZM-coating. The stainless steel bolt was unaffected.

After the full test of six weeks, the combination of the ZM-coatedprofile and the galvanized CW 8.8 bolt showed some white corrosion ofthe ZM-coating, and the entire bolt was corroded and showed a lot of redrust.

After the full test of six weeks, the combination of the ZM-coatedprofile and the galvanized HBS 8.8u bolt showed some white corrosion ofthe ZM-coating, and the bolt showed quite some red rust and whiteoxides.

After the full test of six weeks, the combination of the ZM-coatedprofile and the batch galvanized NORM bolt showed hardly any whitecorrosion of the ZM-coating, but the bolt was covered with white oxides.

After the full test of six weeks, for the combination of the ZM-coatedprofile and the electrically galvanized JD 8.8, the bolt showed a lot ofred rust.

After the full test of six weeks, the combination of the ZM-coatedprofile and the bolt with the aluminum manganese coating according tothe invention showed no white corrosion or other degradation of theZM-coating. The bolt had some red rust, but upon closer inspection itshowed that this was only at places where the coating did not adhere tothe bolt. Where the coating was present, no degradation of the coatingwas observed.

FIG. 8 shows the result of accelerated corrosion tests in which thebolts as such were subjected to a humid and saline environment. Thistest is mainly directed at determining the resistance against corrosiondue to the direct contact with the humid and saline environments. Nogalvanic corrosion was induced in this test.

The test cycle and the types of bolts that were tested were the same asfor the galvanic corrosion test of which FIGS. 6 and 7 show the results.

Column A of FIG. 8 shows the situation at the start of the test. ColumnB of FIG. 8 shows the situation after one week and column C of FIG. 8shows the situation after six weeks, so at the end of the test. Withrespect to the with the aluminum manganese coating according to theinvention, it must be noted that only the top of the bolt, which is thepart enclosed by the box “a” in column C of FIG. 8, was provided withthe aluminum manganese coating according to the invention.

The stainless steel bolt came out of this test rather clean. It was notaffected by corrosion.

Also the bolt that was coated with the aluminum manganese coatingaccording to the invention came out of the test with hardly anycorrosion, at least on the part of the bolt that was coated with thealuminum manganese coating according to the invention.

The galvanized bolt indicated as “HBS 8.8U” came out of the test with alot of white oxides on its surface.

The galvanized bolts indicated as “CW 8.8” and “JD 8.8” came out of thetest covered with red rust.

The galvanized bolt indicated as “NORM 8.8” came out of the test withwhite oxides on its surface, although less than the bolt “HBS 8.8U”showed.

1. A structure for use in a corrosive environment, comprising: a primarystructural element, which primary structural element is made of metaland is provided with a coating, which coating has a compositioncomprising zinc in a content of at least 40 wt % based on the weight ofthe coating, a secondary structural element, which secondary structuralelement is made of metal and is provided with a coating, which coatingis an alloy comprising aluminum and manganese, in which alloy thecontent of aluminum and manganese together is at least 90 wt % based onthe weight of the coating, which alloy comprises more aluminum thanmanganese by weight, and, wherein the primary structural element and thesecondary structural element are in electrical contact with each other.2. The structure according to claim 1, wherein the metal of the primaryand/or the secondary structural element is steel.
 3. The structureaccording to claim 2, wherein the metal of the primary structuralelement and/or the secondary structural element is steel with a carboncontent of 0.5% or less.
 4. The structure according to claim 2, whereinthe metal of the primary structural element and/or the secondarystructural element is low alloy steel.
 5. The structure according toclaim 1, wherein the structure comprises multiple primary structuralelements, at least two of said primary structural elements beingconnected to each other by the secondary structural element.
 6. Thestructure according to claim 1, wherein the primary structural elementis one of a beam, a profile, a strip, a rod, or a sheet.
 7. Thestructure according to claim 1, wherein the secondary structural elementis a support or a fastener.
 8. The structure according to claim 1,wherein the structure further comprises a functional device, wherein thefunctional device is connected to the primary structural element by thesecondary structural element.
 9. The structure according to claim 8,wherein the functional device is one of a solar panel, a switch box, acable, a sensor, or an exhaust system.
 10. The structure according toclaim 1, wherein the aluminum content in the coating of the secondarystructural element is at least about 75 wt % based on the weight of thecoating.
 11. The structure according to claim 1, wherein the aluminumcontent in the coating of the secondary structural element is at leastabout 75 wt % based on the weight of the coating, and at least about 80wt % of the remainder of the coating is manganese.
 12. The structureaccording to claim 10, wherein the coating of the secondary structuralelement comprises about 81-83 wt % aluminum and about 19-17 wt %manganese, based on the weight of the coating, or wherein the coating ofthe secondary structural element comprises about 84-86 wt % aluminum andabout 16-14 wt % manganese, based on the weight of the coating, orwherein the coating of the secondary structural element comprises about94-96 wt % aluminum and about 6-4 wt % manganese, based on the weight ofthe coating.
 13. The structure according to claim 1, wherein a thicknessof the coating of the secondary structural element is between about 1.5μm and about 100 μm.
 14. The structure according to claim 1, wherein thecoating of the primary structural element is a zinc coating having atleast about 90 wt % of pure zinc, a zinc-iron alloy coating, azinc-aluminum alloy coating, a zinc-magnesium alloy coating, analuminum-zinc alloy coating.
 15. The structure according to claim 14,wherein the coating of the primary structural element is a hot-dipcoating.
 16. A method for manufacturing a structure, which methodcomprises: providing a first metal substrate, providing the first metalsubstrate with a coating having a composition comprising zinc in acontent of at least 40 wt % based on the weight of the coating, therebyobtaining a primary structural element, providing a second metalsubstrate, arranging the second metal substrate in a bath of ionicliquid, etching the second metal substrate, providing a source ofaluminum and manganese, electrochemically depositing a coating from theionic liquid onto the second metal substrate, which coating is an alloycomprising aluminum and manganese, in which alloy the content ofaluminum and manganese together is at least 90 wt % based on the weightof the coating, which alloy comprises more aluminum than manganese byweight, thereby obtaining a secondary structural element, and connectingthe primary structural element and the secondary structural element toeach other such that the primary structural element and the secondarystructural element are in electrical contact with each other.
 17. Amethod according to claim 16, wherein the etching of the second metalsubstrate roughens a surface of the second metal substrate and/orremoves oxides and/or contaminants from the surface of the secondsubstrate.
 18. The method according to claim 16, wherein the ionicliquid is a combination of 1-ethyl-3-methylimidazoliumchloride (EMIMCl)and aluminum chloride (AlCl₃), and further comprises MnCl₂.
 19. Themethod according to claim 16, wherein the etching of the second metalsubstrate and the electrochemical deposition of the coating of an alloycomprising aluminum and manganese are carried out in a same bath ofionic liquid.
 20. The method according to claim 16, wherein the etchingof the second metal substrate is electrochemical etching.
 21. The methodaccording to claim 20, wherein the electrochemical etching of the secondmetal substrate is carried out at a voltage between about 0.5 V andabout 1.5 V versus an aluminum electrode.
 22. The method according toclaim 16, wherein the electrochemical deposition of the coating, whichis the alloy comprising aluminum and manganese, has a process parameterwhich is the current density, which current density is between about 2A/dm² and about 7 A/dm².
 23. The method according to claim 16, whereinprior to the etching of the second metal substrate, the second metalsubstrate is cleaned and/or degreased.
 24. The method according to claim16, wherein the coating of the primary structural element is applied inat least one of the following ways: by immersing the first metalsubstrate in a molten bath containing a zinc content of at least about99 wt %, by applying a zinc coating by immersing the first metalsubstrate in a molten bath containing a zinc content of at least about99 wt % and a subsequent annealing which produces an iron-zinc coatingwith an iron content of normally about 8 wt % to about 12 wt % based onthe weight of the coating, by immersing the first metal substrate in amolten bath which is composed of zinc and approximately 5 wt % aluminumand small amounts of mischmetal, by passing the first metal substratethrough a molten zinc bath with aluminum and magnesium contents in sumof about 1.5 wt % to about 8 wt %, by immersing the first metalsubstrate in a molten bath which is composed of about 55 wt % aluminum,about 1.6 wt % silicon and the balance zinc.
 25. The method according toclaim 16, wherein a material of the first metal substrate and/or thesecond metal substrate is steel with a carbon content of 0.5% or less.26. The method according to claim 16, wherein a material of the firstmetal substrate and/or the second metal substrate is low alloy steel.27. A mounting system for a solar panel, which mounting system comprisesat least one structure according to claim
 1. 28. A vehicle comprising atleast one structure according to claim 1.